In most machining operations involving turning a workpiece, it is necessary to securely fix the workpiece in place upon a rotary table or other rotary work surface. Examples of such surfaces to which workpieces are secured include rotary tables, mill tables, fixtures or face plates and lathes, etc. Usually, the workpiece must be secured upon the surface to expose a selected portion of the workpiece upon which work such as cutting or machining is to be performed. In addition to securely fixing the workpiece in place, it is often necessary or desirable to provide fine adjustment in the position and alignment of the workpiece. For example, when a workpiece is secured to a rotary table, accurate alignment of a selected portion of the workpiece with the axial center of the rotary table is desired to facilitate and accurately conduct machine operations upon the workpiece.
Prior to any machining operations, it is necessary to align the part to be machined with the center of rotation of the machine tool. This is particularly difficult for machining large diameter workpieces, such as turbine rotors, on vertical turret lathes. Typically, such workpieces are held in 3-jaw or 4-jaw chucks which are mounted to rotary tables and aligned to the axis of the rotary table. Because of the critical nature of such workpieces, it may be necessary to align them to small tolerances such as within 0.002″ or less. This procedure is very time consuming and, therefore, very costly.